Mechanical Properties and Interfacial Tribological Mechanisms of Silver-Doped 316L Stainless Steel Under Cryogenic Conditions

Abstract High-performance stainless steels have been utilized in reusable rockets to achieve significant reductions in manufacturing and maintenance costs. In this study, the effect of silver doping on the mechanical and tribological properties of 316L stainless steel under cryogenic conditions was experimentally investigated. Three silver mass concentrations of 5 wt%, 10 wt%, and 15 wt%, were selected, and the corresponding microstructural characteristics were analyzed using optical microscopy, energy-dispersive spectroscopy, and electron backscatter diffraction. The cryogenic environment of rocket turbopumps was simulated by immersing the specimens in liquid nitrogen. Rockwell hardness, impact fatigue strength, and tribological performance were subsequently evaluated under both room-temperature and low-temperature conditions, with additional tribological tests conducted under water lubrication for comparison. The results indicated that silver preferentially segregated at austenite grain boundaries, leading to grain refinement and the formation of ductile accommodation regions within the hardened matrix. Silver doping enhanced cryogenic ductility and impact fatigue resistance by promoting plastic deformation capability. Owing to the intrinsic lubricating properties of silver, a self-lubricating film was formed at the sliding interfaces, resulting in reduced friction coefficients and wear-rates. Although silver addition slightly reduced hardness and toughness, its grain-stabilizing effect and interfacial lubricity led to an overall improvement in the cryogenic performance of 316L stainless steel. This work provides useful insights for the development of durable and highly reliable materials for reusable rockets and other cryogenic engineering applications.